thermodynamics

• Thermodynamics


  The branch of heat that deals with the laws of transformation of heat into other forms of energy such as mechanical, chemical and electrical energy and vice versa
• Thermodynamics


  • Principally it is based on two laws of thermodynamics i.e. the first and second laws of thermodynamics
  • It is a practical subject that explains the working of heat engines, refrigerators and heat pumps etc.
• System


  The quantity of matter or region of space whose behavior is being studied
• Surroundings


  Everything other than the system in the universe
• Boundary


  The imagined wall that separates the system and the environment
• Closed system


  The system in which there is no transfer of mass across its boundary
• Open system


  The system in which there is a transfer of mass across its boundary
• The first thermodynamic textbook was written in 1859 by William Ranking, originally trained as a physicist and a civil and mechanical engineering professor at the University of Glasgow
• Thermal equilibrium


  When two objects at different temperatures are brought into contact with each other, energy is transferred from the hotter to the colder object until the bodies reach the same temperature
• Heat is energy transferred spontaneously due to a temperature difference
• If two objects are in thermal equilibrium, they have the same temperature
• Two bodies, one hot and the other cold, are kept in vacuum


  The temperature of the hot body decreases after some time
• Work


  Work is done by a system when the system as a whole expands, and the system exerts a force on the surroundings and thereby displaces the surroundings
• The temperature of a dead person is lower than the temperature of a normal healthy person
• Internal energy


  The sum of the kinetic and potential energies associated with the random motion of the atoms of the substance
• The temperature of a normal healthy old man is less than that of a normal healthy young man
• When ice melts in a glass of water, the water level remains the same
• Heat


  Energy which is transferred between a substance and its surroundings or between one part of a substance to another as a result of temperature difference only
• Mechanical equivalent of heat

  The ratio of the work done in joules to the heat produced in calories
• The currently accepted value of mechanical equivalent of heat is 4.18 joule per calorie
• Joule's experiment showed that there is a definite relationship between the mechanical work done and the heat generated
• An empty polythene bag burns or melts on a flame of a stove, but water filled polythene bag can be used to make tea by placing it on a flame of a stove
• An ink dot on a white porcelain dish appears darker than the surroundings, but when the dish is raised to a very high temperature, the dot appears brighter than the surroundings
• Closed system


  A system in which there is no transfer of mass across its boundary
• Closed system


  • The transfer of heat energy can take place from the system to the surrounding or vice versa
• Closed system


  • Hot food in a pressure cooker
• An ink dot on a white porcelain dish appears dark. When the dish is raised to a very large temperature the dot appears brighter than the surroundings.
• Normally, a system must have some interactions with its surroundings.
• Open system


  A system in which there is a transfer of mass across its boundary
• Open system


  • The transfer of heat energy can take place from the system to the surrounding or vice versa
• Open system


  • Boiling tea kettle
• Isolated system


  A system in which there is no transfer of mass and heat energy across its boundary
• In an isolated system both mass and energy cannot enter or leave the system across its boundary
• Isolated system


  • Tea contained in a well insulating thermo flask
• Thermodynamic state


  The particular condition when a system has specified values of pressure P, volume V and temperature T
• Thermodynamic state variables


  Variables or functions which determine the physical state of the system
• If the system is homogeneous, it is usually enough to specify only three parameters: volume, pressure and temperature
• Equation of state


  The mathematical relationship between pressure, volume and temperature for an ideal gas: PV = nRT
• The exact relationship between pressure, volume and temperature is not known for solids, liquids and non-homogeneous substances
• Other examples of state variables are internal energy U and entropy S